In conventional swimming pools the surface layer of water is drawn off via skimmer boxes built into the top of the side walls of the pool. The water is filtered in the box to remove any litter floating on the surface and returned to the pool via nozzles which are usually located in the pool wall opposite the skimmer box. There are also devices used in conjunction with skimmer boxes which crawl over the floor and walls of the pool sucking up debris into the filter in the skimmer box.
However the problem with conventional skimmer boxes is that they only skim effectively when the surface level of the pool is kept within a narrow range, usually less than 80 mm. Accordingly if the level falls below the bottom ledge of the box opening no water is removed from the pool. Or if the level rises above the box opening, the sub-surface water is removed and litter is left floating on the surface.
A variety of devices have been developed to skim the surface water from pools where the water level varies over a wide range. For example U.S. Pat. No. 4,325,150 has an inner concentric cylinder containing a strainer basket and floats within an outer concentric cylinder which attaches to a suction hose. U.S. Pat. No. 4,212,740 has a similar construction but has a weir, the lip of which floats at the water surface level. However both of these require separate plumbing arrangements and appear to be free floating.
U.S. Pat. No. 6,187,181 and U.S. Pat. No. 5,078,863 teach similar but more complicated arrangements of the above constructions while WO 97/49882 discloses a suction powered automatic crawler the buoyancy of which can be adjusted so that it floats at the surface of the water and skims the surface layer. However all of these arrangements involve many moving parts and are prone to failure requiring heavy maintenance.
The device of U.S. Pat. No. 4,501,659 has a semi cylindrical outer body mounted on the pool wall and an inner mating semi cylindrical body floating within it. It is superficially similar to the device of the present invention but works on a quite different principle. Water is injected into the bottom of the outer body from a nozzle protruding from the pool wall and passes out through a nozzle in the opposite cylindrical wall of the outer body. This is said to create a reduction in pressure at the base of the outer body and water is drawn into the floating body from the surface of the pool. It is designed to be fitted over an existing high pressure water jet in the wall of the pool and not at a suction skimmer box as the present invention.